Optimizing the defect engineering of MnCo2O4 spinel structure through Zn-substitution as a cathode for high-performance Zinc-ion batteries

Abstract

Zinc-ion batteries are regarded as an effective alternative for energy storage because of their low flammability, affordability, inherent safety, and high theoretical capacity. However, manganese-based materials are limited due to a relatively narrow tunneling pathway, causing low-rate capacity and low life cycle stability. Hence, an effective strategy using defect-engineered crystal structure promoted by Zn-substituted MnCo2O4 to achieve a high-performance ZIB is proposed. The microspheres, assembled with interconnected micro- and nanoflake structures of ZnxMn1-xCo2O4 (with the Zn-substitution of x = 0, 0.2, 0.4, 0.6, and 0.8), are hydrothermally synthesized, followed by calcination, which serves as the cathode for ZIBs. At the optimal Zn0.4Mn0.6Co2O4 cathode, ZIBs battery possesses a superior discharged specific capacity of 660 mAh g-1 at 0.05 A g-1, a high-rate performance (energy density of 260–528 Wh kg−1 at a power density of 800–40 W kg−1), and good capacity retention of 70 mAh g-1 after 800 cycles at 0.2 A g–1. Ex-situ SEM-EDX and XPS results through charge/discharge cycles confirm the high stability and reversibility of Zn0.4Mn0.6Co2O4 in its electron state. Such improved rate capacity and long-life cycles originate from efficient defect engineering using Zn-substitution and oxygen vacancies. These lead to improved ion insertion and Zn2+ transport kinetics, along with enhanced electrical conductivity, resulting in the reversibility reactions of Mn4+/Mn2+ and Co2+/Co3+ upon Zn2+insertion/extraction.